Screw for molding thermoplastic resin having a stress relaxation section

Abstract

This invention relates to a screw used in an equipment for molding thermoplastic resin, in which a mixing section is provided at a position adjacent a shearing section, and the pitch of a stress relaxation section is preset to the pitch, at which satisfactory kneading can be performed without giving high shearing to the resin. With this screw, even if high-speed extrusion molding is performed, the pressure of resin is not fluctuated, molded parts can avoid lowered material quality and outstanding molded parts can be provided.

What is claimed is: 
     
       1. A screw for molding thermoplastic resin, comprising: a feed section, a compression section which is a relaxed compression section having a compression ratio in the range of 3 or less, a shearing section and a stress relaxation section being successively provided from a resin feed side to a resin extrusion side, and a mixing section being provided intermediate said shearing section and said stress relaxation section, the length of said shearing section being in the range of 0.2-2 times the diameter of said screw, the length of said stress relaxation section being in the range of 4-15 times the diameter of said screw, and a ratio L/D between the total length L and the diameter D of said screw being in the range of 15-40. 
     
     
       2. A screw for molding thermoplastic resin as set forth in claim 1, wherein said feed section is a straight screw having a compression ratio of 1. 
     
     
       3. A screw for molding thermoplastic resin as set forth in claim 1, wherein said compression ratio is in the range of 2.5 or less. 
     
     
       4. A screw for molding thermoplastic resin as set forth in claim 1, wherein said shearing section is a torpedo. 
     
     
       5. A screw for molding thermoplastic resin as set forth in claim 1, wherein the length of said shearing section is in the range of 0.3-1.5 times the diameter of said screw. 
     
     
       6. A screw for molding thermoplastic resin as set forth in claim 1, wherein said mixing section is contiguous with said shearing section on said resin extrusion side. 
     
     
       7. A screw for molding thermoplastic resin as set forth in claim 1, wherein said mixing section comprises gear wheels. 
     
     
       8. A screw for molding thermoplastic resin as set forth in claim 7, wherein said plurality of said gear wheels are spaced a predetermined distance apart from one another, and the outer diameter of said gear wheels is equal to the outer diameter of said shearing section. 
     
     
       9. A screw for molding thermoplastic resin as set forth in claim 1, wherein mixing sections are provided at opposite axial ends of said shearing section. 
     
     
       10. A screw for molding thermoplastic resin as set forth in claim 9, wherein said mixing sections each comprise gear wheels. 
     
     
       11. A screw for molding thermoplastic resin, comprising: a feed section, a compression section, a shearing section and a stress relaxation section are successively provided from a resin feed side to a resin extrusion side, said screw having at least one thread in each of said sections, the pitch of at least part of said thread in said stress relaxation section being in the range of 0.3-0.8 times the pitch of the thread in at least one of said feed section and said compression section, and a ratio L/D between the total length L and the diameter D of said screw is in the range of 15-40. 
     
     
       12. A screw for molding thermoplastic resin as set forth in claim 11, wherein said stress relaxation section has a compression ratio in the range of 2-0.5. 
     
     
       13. A screw for molding thermoplastic resin as set forth in claim 11, wherein said stress relaxation section has a compression ratio in the range of 1.6-0.8. 
     
     
       14. A screw for molding thermoplastic resin as set forth in claim 11, wherein a mixing section is contiguous with said shearing section on said resin extrusion side. 
     
     
       15. A screw for molding thermoplastic resin as set forth in claim 11, wherein a mixing section is contiguous with said shearing section on said resin feed side. 
     
     
       16. A screw for molding thermoplastic resin as set forth in claim 11, wherein mixing sections are provided at opposite axial ends of said shearing section on both the resin extrusion and the resin feed sides, respectively. 
     
     
       17. A screw for molding thermoplastic resin as set forth in claim 16, wherein said mixing section comprises gear wheels.